1. Field of the Invention
The invention relates to a fluid power actuator comprising a cylinder, a piston, a piston rod and a positioning means for halting the piston rod in desired positions.
2. Description of Prior Art
Such actuators are employed for applications in which a variable, preset terminal position of the piston and of the piston rod is necessary. Terminal abutments arranged in the caps of the actuator cylinder are able to be screwed into the interior of the cylinder varying amounts so as to limit the stroke of the piston to a certain extent. Such actuators are however relatively high in price since they are generally specially customized and in any case are of a complex design; in fact it is more or less essential to have a damper at the end of the stroke so that the terminal abutments will not be damaged by the piston striking them. A further shortcoming is that known actuators only make it possible for two abutment positions to be set with one position at a more or less retracted position of the piston rod and the other in a more or less extended one, and between these two end settings it is nearly impossible to preset exact intermediate positions of the piston or its rod at which such components may be precisely halted, at least for an instant. However in many applications it is essential to have an actuator whose piston rod may be moved in exact steps or sections of stroke, as for example when the actuator is to be used for a feed device in a machine tool, with which the workpieces are to have machining operations carried out on them, such as drilling or stamping, at positions with a precise setting between them.